I was looking at Sigma APO 135-400mm F4.5-5.6 AF (I found it for good price), but I think it's quite old lens. It interests me because of it's focal length and I'm thinking about buying it instead of current lens.

I want to ask: What would be difference between Sigma and Nikkor lens? Except VR and focal length. Could there be some problem with my D3100? Could it be slower or less acurate (auto-focus)? Could there be some difference in resulting image (colors, sharpness) because of lens age? Can I have any problems shooting from hands without VR?

2 Answers
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Well, it won't autofocus on a D3100. Because it doesn't have a built-in focus motor ("AF-S" for Nikon, "HSM" for Sigma) it's manual focus only. This lens will autofocus with bodies that have an AF motor, such as the D7000 and D300S. The 3100 body does not have an AF motor built in, and so only autofocus with "AF-S" or "HSM" lenses with a motor in the lens.

This is an older lens, and has since been replaced by the 120-400, which does have HSM, so would focus on your D3100.

Could there be some difference in resulting image (colors, sharpness) because of lens age?

In general, older lenses perform less well than their modern equivalents. I haven't used this lens so I can't say if the performance would be disappointing, but if you search for some reviews I'm sure you can figure this out.

Can I have any problems shooting from hands without VR?

Many lenses don't have VR. You may need to rely on proper technique and/or support to get sharp photos, but that will depend upon the environment and subject.

Well, let me clarify my answer: this lens will autofocus with bodies that have an AF motor, such as the D7000 and D300S. The 3100 body does not have an AF motor built in, and so only autofocus with "AF-S" or "HSM" lenses with a motor in the lens.
– Dan WolfgangJun 18 '12 at 14:12

I would go with ultra-cheap Tamron 70-300 OS or Nikon 70-300VR. I think they're both of equal design. At least that's word on street that they were from same specifications. Both are great for DX cams. Also, the 55-300, I believe, is good. Lost track of DX lens lineup. Just get VR in whichever lens because handholding without blur is nearly impossibly at longer lengths.